This invention pertains to porous hollow fiber membranes.
Hollow fiber membranes are generally defined as having an inside surface, an outside surface, and defining a wall and a hollow cavity or bore. They are typically arranged in a filter device as a plurality or bundle of fibers, and utilized for a variety of filtration applications. In some filtration applications, referred to as xe2x80x9cinside-outxe2x80x9d flow applications, the hollow fiber membranes in the filter device each have small pores at the inner surface and large pores at the outer surface, and the fluid to be filtered is passed through the inlet of the device into the bores of the membranes such that a portion of the fluid is passed from the inside surface of the fiber to the outside surface and through one outlet of the device, and another portion passes tangentially or parallel to the inside surface and through another outlet of the device. The fluid passing into the device and bore of the membrane is commonly referred to as the feed (the feed contains various sized molecules and/or species and possibly debris), the fluid passing from the inside surface to the outside surface is commonly referred to as the permeate or the filtrate (the permeate or filtrate contains the smaller molecules and/or species that will pass through the pores of the membrane), and the fluid passing parallel to the inside surface of the membrane without passing to the outside surface is commonly referred to as the retentate (the retentate contains the larger molecules that do not pass through the pores of the membrane).
Conventional hollow fiber membranes used in inside-out applications have suffered from a number of deficiencies, particularly due to fouling of the inside surface. Fouling typically refers to the accumulation of material on the inside surface of the membrane. This accumulated material can block the pores of the membrane, thus preventing or reducing the passage of the desired product or molecules into the permeate. Once the surface is fouled, filtration efficiency is decreased, and the fibers need to be cleaned or replaced. Additionally, some membranes are difficult to clean. These problems can be magnified in filter devices including a plurality of hollow fibers, since some fibers can become more heavily fouled than others, resulting in uneven flow.
The present invention provides for ameliorating at least some of the disadvantages of the prior art. These and other advantages of the present invention will be apparent from the description as set forth below.
In accordance with an embodiment of the invention, a porous hollow fiber membrane is provided comprising convoluted inner and/or outer porous surfaces. In more preferred embodiments, the convoluted inner and/or outer surfaces are in the form of a sinusoidal shape over an arc.
Hollow fiber membranes having at least one convoluted surface, preferably at least a convoluted inside surface, have improved capacity over typical hollow fiber membranes in that the inventive membranes have increased surface area available for filtration. The convoluted porous surfaces are permeable, e.g., active, in that fluid passes through the surfaces. Such porous membranes are particularly useful in filter devices used for tangential flow filtration applications, but can also be utilized in dead end (also referred to as direct flow) filtration applications, wherein the devices include filters having a plurality of hollow fibers.